Kawano Tomonori, Kadono Takashi, Furuichi Takuya, Muto Shoshi, Lapeyrie Frédéric
Graduate School of Environmental Engineering, The University of Kitakyushu, Kitakyushu 808-0135, Japan.
Biochem Biophys Res Commun. 2003 Aug 15;308(1):35-42. doi: 10.1016/s0006-291x(03)01286-5.
Trivalent cations such as those of Al, La, and Gd are phytotoxic. Our previous works showed that addition of LaCl(3) or GdCl(3) to tobacco cells triggers the generation of superoxide (O(2)-). Here, we show that AlCl(3) at normal physiological pH (5.8) induces much greater production of O(2)- (detected with a specific chemiluminescence probe), indicating that these trivalent cations similarly induce the oxidative bursts. It was shown that NADPH oxidase is involved in the generation of O(2)- and the yield of O(2)- was dose-dependent (ca. 6mM Al, optimal). Following the acute spike of O(2)-, a gradual increase in cytosolic-free Ca(2+) concentration (Ca(2+)) was detected with the luminescence of recombinant aequorin over-expressed in the cytosol. Interestingly, a O(2)- scavenger and a Ca(2+) chelator significantly lowered the level of Ca(2+) increase, indicating that the Al-induced O(2)- stimulates the influx of Ca(2+). Compared to the induction of O(2)- generation, the Ca(2+) elevation was shown to be maximal (340 nM) at relatively lower Al concentrations (ca. 1.25 mM). Thus, the Al concentration optimal for O(2)- is too much (inhibitory) for Ca(2+). In addition, high concentrations of Al were shown to be inhibitory to the H(2)O(2)-induced Ca(2+) influx. This explains the ineffectiveness of high Al concentration in the oxidative burst-mediated induction of Ca(2+) increase. It is likely that Al-induced Ca(2+) elevation is manifested from the finely geared balance between the O(2)- -mediated driving force and the channel inhibition-mediated brake. Furthermore, it is note-worthy that Al (< or =10mM) showed no inhibitory effect on the hypo-osmolarity-induced Ca(2+) influx, implying that Al may be a selective inhibitor of redox-responsive Ca(2+) channels. Possible target channels of Al actions are discussed.
三价阳离子，如铝、镧和钆的阳离子具有植物毒性。我们之前的研究表明，向烟草细胞中添加氯化镧（LaCl₃）或氯化钆（GdCl₃）会引发超氧阴离子（O₂⁻）的产生。在此，我们表明在正常生理pH值（5.8）下，氯化铝（AlCl₃）诱导产生的O₂⁻（用特定的化学发光探针检测）要多得多，这表明这些三价阳离子同样会诱导氧化爆发。研究表明，NADPH氧化酶参与了O₂⁻*的产生，且O₂⁻*的产量呈剂量依赖性（约6mM铝时最佳）。在O₂⁻*急性峰值出现后，通过在细胞质中过表达的重组水母发光蛋白的发光检测到细胞质游离钙离子浓度（[Ca²⁺]c）逐渐增加。有趣的是，一种O₂⁻*清除剂和一种钙离子螯合剂显著降低了[Ca²⁺]c增加的水平，这表明铝诱导的O₂⁻*刺激了钙离子内流。与O₂⁻*产生的诱导相比，在相对较低的铝浓度（约1.25mM）下，[Ca²⁺]c升高达到最大值（340 nM）。因此，对O₂⁻*而言最佳的铝浓度对[Ca²⁺]c来说过高（具有抑制作用）。此外，高浓度的铝被证明对过氧化氢诱导的钙离子内流具有抑制作用。这解释了高铝浓度在氧化爆发介导的[Ca²⁺]c增加诱导中无效的原因。铝诱导的[Ca²⁺]c升高可能是由O₂⁻*介导的驱动力和通道抑制介导的制动之间精确调节的平衡所导致的。此外，值得注意的是，铝（≤10mM）对低渗诱导的钙离子内流没有抑制作用，这意味着铝可能是氧化还原反应性钙离子通道的选择性抑制剂。文中讨论了铝作用的可能靶通道。
